Polyolefin-based resin pre-expanded particles and polyolefin-based resin in-mold expansion molded article comprising polyolefin-based resin pre-expanded particles

ABSTRACT

Polyolefin-based resin pre-expanded particles include a polyolefin-based resin composition including a polyolefin-based resin, a sterically hindered amine ether flame retardant expressed by the general formula (1): R 1 NHCH 2 CH 2 CH 2 NR 2 CH 2 CH 2 NR 3 CH 2 CH 2 CH 2 NHR 4  (1), and a phosphoric ester. The polyolefin-based resin pre-expanded particles are flame retardant polyolefin-based resin pre-expanded particles that can have good in-mold expansion moldability and exhibit excellent flame resistance compared to the conventional pre-expanded particles even when molded into a sample having a higher density or a larger thickness without using a halogen flame retardant, and that do not generate harmful gas during burning.

TECHNICAL FIELD

The present invention relates to polyolefin-based resin pre-expandedparticles that have flame resistance and are used for the production ofa heat insulating material, a cushioning packaging material, areturnable container, an automotive bumper core, electrical andelectronic products/components, or the like, and particularly theproduction of the electrical and electronic products/components. Thepresent invention also relates to a polyolefin-based resin in-moldexpansion molded article produced by in-mold expansion molding of thepolyolefin-based resin pre-expanded particles.

BACKGROUND ART

An in-mold expansion molded article is characterized by arbitrary shape,lightweight, heat insulating properties, etc. In particular, an in-moldexpansion molded article obtained from polyolefin-based resinpre-expanded particles is superior to an in-mold expansion moldedarticle obtained from polystyrene-based resin pre-expanded particles inchemical resistance, heat resistance, and a distortion restoration rateafter compression. Because of these characteristics, the in-moldexpansion molded article obtained from the polyolefin-based resinpre-expanded particles has been put to various uses such as anautomotive interior material, an automotive bumper core, a heatinsulating material, and a cushioning packaging material.

However, the expansion molded article made of a polyolefin-based resingenerally has the disadvantage of being flammable, although it has theexcellent properties as described above. In particular, the expansionmolded article has high flammability and burns easily compared to anon-expansion molded article.

In recent years, there is a growing demand for automotive parts,building materials, and electrical and electronic products/componentshaving flame resistance and self-extinguishing properties. To meet thedemand, many studies have been conducted on the expansion moldedarticles with flame resistance.

Various methods for imparting flame resistance to the inherentlyflammable polyolefin-based resin are being studied, and a flameretardant is added in general. Various flame retardants such as ahalogen-containing compound, a hydrated metal oxide, phosphoric esters,and a nitrogen-containing compound have been used for thepolyolefin-based resin.

Patent Document 1 discloses adding a sterically hindered amine etherflame retardant (a non-halogen flame retardant) to polyolefin-basedresin pre-expanded particles, thereby providing an in-mold expansionmolded article that meets HF-1 according to the UL94 horizontal burningtest for foamed materials without causing a problem such as thedeterioration of the in-mold expansion moldability, as shown inExamples. Patent Document 2 discloses an in-mold expansion moldedarticle that uses the same flame retardant as that disclosed in PatentDocument 1 and shows self-extinguishing properties in the burning testbased on FMVSS302. In general, the polyolefin-based resin in-moldexpansion molded article having a higher density or a larger thicknessburns more easily. Therefore, even with the use of the stericallyhindered amine ether flame retardant, it is desired that the flameretardant performance be further improved.

Patent Document 3 discloses a flame retardant polypropylene fiber and aflame retardant polypropylene film that include 0.5 wt % or more of aphosphoric ester-based flame retardant and 0.4 wt % or more of an NORtype hindered amine-based stabilizer. Patent Document 4 discloses aflame retardant that includes a metal hydroxide, a hindered aminecompound having a piperidine skeleton, and a phosphoric ester. However,the production processes of the polyolefin-based resin pre-expandedparticles and the in-mold expansion molded article thereof involve,e.g., the impregnation of the resin particles with a blowing agent,heating, rapid pressure release, and heating with steam. Therefore,there is concern that decomposition of the flame retardant or a reactiondue to the addition of the flame retardant may occur. Moreover, thepolyolefin-based resin pre-expanded particles are filled into a mold,heated with steam or the like, and fused together to form an in-moldexpansion molded article. In this case, if the moldability isdeteriorated due to the properties of the pre-expanded particles, acommercial value of the molded article is significantly reduced. Theadditives mixed with the polyolefin-based resin can affect, e.g., theshape and size of cells, the interconnection between the cells, and thefusion of the pre-expanded particles, and thus such changes may resultin the deterioration of the in-mold expansion moldability and themechanical strength.

Patent Document 5 discloses flame retardant polyolefin-based resinpre-expanded particles that include a pentavalent phosphate compoundcontaining halogen. However, the use of halogen-containing materials hasbeen restricted in recent years. Moreover, a halogenated phosphoricester differs from a non-halogenated phosphoric ester in degradability,compatibility with the resin, or the like. Further, Patent Document 5discloses the addition of a flame retardant aid, but does not disclosethe addition of the other flame retardants.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: WO 2003/048239-   Patent Document 2 JP 2004-263033 A-   Patent Document 3: JP 2001-348724 A-   Patent Document 4: JP 2006-316168 A-   Patent Document 5: JP H9 (1997)-227711 A

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

It is an object of the present invention to provide flame retardantpolyolefin-based resin pre-expanded particles that can have good in-moldexpansion moldability and exhibit excellent flame resistance compared tothe conventional pre-expanded particles even when molded into a samplehaving a higher density or a larger thickness without using a halogenflame retardant, and that do not generate harmful gas during burning.

Means for Solving Problem

As a result of a detailed study conducted in view of the above problems,the present inventors found out that when the polyolefin-based resinpre-expanded particles are formed of a polyolefin-based resincomposition including a sterically hindered amine ether flame retardantand a phosphoric ester, the polyolefin-based resin pre-expandedparticles can have good in-mold expansion moldability and exhibitexcellent flame resistance compared to the conventional pre-expandedparticles, specifically excellent flame resistance even in the case ofan in-mold expansion molded article having a higher density or a largerthickness.

The present invention has the following configuration.

[1] Polyolefin-based resin pre-expanded particles including apolyolefin-based resin composition including:

a polyolefin-based resin;

a sterically hindered amine ether flame retardant expressed by thefollowing general formula (1):

R¹NHCH₂CH₂CH₂NR²CH₂CH₂NR³CH₂CH₂CH₂NHR⁴  (1)

(where R¹, R² and one of R³ and R⁴ are an s-triazine moiety T expressedby the following general formula (2):

the other of R³ and R⁴ is a hydrogen atom, and in the general formula(2), R⁵ is an alkyl group having 1 to 12 carbon atoms and R⁶ is a methylgroup, a cyclohexyl group, or an octyl group); and

a phosphoric ester

[2] The polyolefin-based resin pre-expanded particles according to [1],obtained by dispersing polyolefin-based resin particles composed of thepolyolefin-based resin composition into an aqueous dispersion medium inthe presence of a blowing agent, heating the dispersion thus obtainedunder pressure, and releasing the dispersion into a low pressure region.

[3] The polyolefin-based resin pre-expanded particles according to [1]or [2], wherein the phosphoric ester is an aromatic-based phosphoricester.

[4] The polyolefin-based resin pre-expanded particles according to anyone of [1] to [3], wherein the blowing agent is at least one selectedfrom the group consisting of isobutane and normal butane.

[5] The polyolefin-based resin pre-expanded particles according to anyone of [1] to [4], wherein the blowing agent is carbon dioxide.

[6] The polyolefin-based resin pre-expanded particles according to anyone of [1] to [5], wherein the polyolefin-based resin compositionincludes 0.01 parts by weight to 20 parts by weight of the stericallyhindered amine ether flame retardant expressed by the general formula(1) and 0.01 parts by weight to 10 parts by weight of the phosphoricester with respect to 100 parts by weight of the polyolefin-based resin.

[7] The polyolefin-based resin pre-expanded particles according to anyone of [1] to [6], wherein the polyolefin-based resin is apolypropylene-based resin.

[8] A polyolefin-based resin in-mold expansion molded article producedby in-mold expansion molding of the polyolefin-based resin pre-expandedparticles according to any one of [1] to [7].

Effects of the Invention

The use of the polyolefin-based resin pre-expanded particles of thepresent invention can provide an in-mold expansion molded article thathas excellent flame resistance compared to the conventional expansionmolded article even in the case of a sample having a higher density or alarger thickness while maintaining good in-mold expansion moldabilityand surface appearance that are comparable to those of the conventionalexpansion molded article.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of a DSC curve obtained when the temperature ofthe polyolefin-based resin pre-expanded particles of the presentinvention is increased from 40° C. to 220° C. at a rate of 10° C./minusing a differential scanning calorimeter (DSC). In FIG. 1, the DSCcurve has a melting peak on the low temperature side and a melting peakon the high temperature side; Ql represents a heat quantity of themelting peak on the low temperature side, i.e., a heat quantityindicated by an area enclosed by the melting peak on the low temperatureside and a tangent line that extends from the maximum point between thelow-temperature peak and the high-temperature peak to the base lineindicating the start of melting; and Qh represents a heat quantity ofthe melting peak on the high temperature side, i.e., a heat quantityindicated by an area enclosed by the melting peak on the hightemperature side and a tangent line that extends from the maximum pointbetween the low-temperature peak and the high-temperature peak to thebase line indicating the end of melting.

DESCRIPTION OF THE INVENTION

The polyolefin-based resin used in the present invention is a polymercontaining 75 wt % or more of an olefin-based monomer. The content ofthe olefin-based monomer is preferably 80 wt % or more. Thepolyolefin-based resin may contain 25 wt % or less, preferably 20 wt %or less of other monomers copolymerizable with the olefin-based monomer.

Specific examples of the olefin-based monomer include α-olefins having 2to 12 carbon atoms such as ethylene, propylene, butene-1, isobutene,pentene-1,3-methyl-butene-1,hexene-1,4-methyl-pentene-1,3,4-dimethyl-butene-1,heptene-1,3-methyl-hexene-1, octene-1, and decene-1. They may be usedindividually or in combination of two or more.

Specific examples of the other monomers copolymerizable with theolefin-based monomer include cyclic olefins such as cyclopentene,norbornene, and1,4,5,8-dimethano-1,2,3,4,4a,8,8a,6-octahydronaphthalene, and dienessuch as 5-methylene-2-norbornene, 5-ethylidene-2-norbornene,1,4-hexadiene, methyl-1,4-hexadiene, and 7-methyl-1,6-octadiene. Theymay be used individually or in combination of two or more.

Specific examples of the polyolefin-based resin used in the presentinvention include polyethylene-based resins containing ethylene as themain component such as high density polyethylene, medium densitypolyethylene, low density polyethylene, and linear low densitypolyethylene, and polypropylene-based resins containing propylene as themain component. These polyolefin-based resins may be used individuallyor in combination of two or more. In particular, the use of thepolypropylene-based resin as the polyolefin-based resin is preferred interms of the mechanical strength, the heat resistance, or the like.

The polypropylene-based resin is not particularly limited as long as itcontains propylene as the main component of the monomer. For example,the polypropylene-based resin can be a propylene homopolymer, anα-olefin-propylene random copolymer, or an α-olefin-propylene blockcopolymer. They may be used individually or in combination of two ormore. In particular; the polypropylene-based resin containing ethylenethat is copolymerized with propylene as a monomer component (i.e., theα-olefin is ethylene) is preferred because it is easily available andhas excellent processing moldability. The content of ethylene in thepolypropylene-based resin is preferably 1 wt % to 10 wt %, morepreferably 2 wt % to 7 wt %, even more preferably 3.5 wt % to 6 wt %,and particularly preferably 3.5 wt % to 5 wt %. The content of ethylenethat is copolymerized with propylene in the polypropylene-based resincan be measured with ¹³C-NMR.

The melting point of the polypropylene-based resin used in the presentinvention is preferably 130° C. to 165° C., and more preferably 135° C.to 155° C. If the melting point of the polypropylene-based resin is lessthan 130° C., the heat resistance and the mechanical strength are notlikely to be sufficient. If the melting point of the polypropylene-basedresin is more than 165° C., it is difficult to ensure the fusion ofbeads in in-mold expansion molding. The melting point is determined inthe following manner. Using a differential scanning calorimeter, thetemperature of 1 to 10 mg of the polypropylene-based resin is increasedfrom 40° C. to 220° C. at a rate of 10° C./min, then reduced to 40° C.at a rate of 10° C./min, and again raised to 220° C. at a rate of 10°C./min, so that a DSC curve is obtained. The melting point is a peaktemperature of the endothermic peak on the DSC curve that is obtainedwhen the temperature of the polypropylene-based resin is again raised to220° C.

The melt flow rate (referred to as “MFR value” in the following) of thepolypropylene-based resin used in the present invention is preferably0.5 g/10 min to 30 g/10 min, and more preferably 2 g/10 min to 20 g/10min. If the MFR value is less than 0.5 g/10 min, it may be difficult toprovide polypropylene-based resin pre-expanded particles with a highexpansion ratio. If the MFR value is more than 30 g/10 min, the cells ofthe polypropylene-based resin pre-expanded particles are easily broken,so that the open-cell ratio of the polypropylene-based resinpre-expanded particles is likely to be high. The MFR value of thepolypropylene-based resin conforms to JIS K7210 and is measured at 230°C. and a load of 2.16 kg.

The ratio (Mw/Mn) of the weight average molecular weight (also referredto as “Mw” in the following) to the number average molecular weight(also referred to as “Mn” in the following) of the polypropylene-basedresin used in the present invention is not particularly limited, but ispreferably 3.0 or more, and particularly preferably 3.0 to 6.0.

The Mn and Mw of the polypropylene-based resin are measured under thefollowing conditions.

Measuring device: Alliance GPC 2000-type gel permeation chromatography(GPC) manufactured by Waters Corporation

Column: TSKgel GMH6-HT (2 columns) and TSKgel GMH6-HTL (2 columns), eachcolumn having an inner diameter of 7.5 mm×a length of 300 mm,manufactured by TOSOH CORPORATION

Mobile phase: o-dichlorobenzene (containing 0.025% BHT)

Column temperature: 140° C.

Flow rate: 1.0 mL/min

Sample concentration: 0.15% (W/V)-o-dichlorobenzene

Injection amount: 500 μL

Molecular weight calibration: polystyrene (i.e., calibration usingpolystyrene standards)

Examples of the polyethylene-based resin used in the present inventioninclude an ethylene homopolymer, an ethylene-α-olefin random copolymer,an ethylene-α-olefin block copolymer, low density polyethylene, highdensity polyethylene, and linear low density polyethylene. In this case,the α-olefins can be those having 3 to 15 carbon atoms, and they may beused individually or in combination of two or more. Among thepolyethylene-based resins, the ethylene-α-olefin block copolymercontaining a comonomer (other than ethylene) in an amount of 1 to 10 wt% or the linear low density polyethylene is preferred because they havegood expandability.

The melting point of the polyethylene-based resin used in the presentinvention is preferably 110° C. to 140° C., and more preferably 120° C.to 130° C. By controlling the melting point in the above range, thepre-expanded particles can have good expandability and moldability, andthus the polyolefin-based resin in-mold expansion molded articleobtained from the pre-expanded particles can have excellent mechanicalstrength and heat resistance. The melting point is determined in thefollowing manner. Using a differential scanning calorimeter, thetemperature of 1 to 10 mg of the polyethylene-based resin is increasedfrom 40° C. to 200° C. at a rate of 10° C./min, then reduced to 40° C.at a rate of 10° C./min, and again raised to 200° C. at a rate of 10°C./min, so that a DSC curve is obtained. The melting point is a peaktemperature of the endothermic peak on the DSC curve that is obtainedwhen the temperature of the polyethylene-based resin is again raised to200° C.

The melt flow rate (referred to as “MFR value” in the following) of thepolyethylene-based resin used in the present invention is preferably 0.5g/10 min to 30 g/10 min, more preferably 1 g/10 min to 5 g/10 min, andmost preferably 1.5 g/10 min to 2.5 g/10 min. If the MFR value is lessthan 0.5 g/10 min, it may be difficult to provide pre-expanded particleswith a high expansion ratio, and the cells tend to be nonuniform. If theMFR value is more than 30 g/10 min, it may be easily expanded, but thecells may be easily broken, so that the open-cell ratio of thepre-expanded particles is likely to be high, and the cells tend to benonuniform. The MFR value of the polyethylene-based resin conforms toJIS K7210 and is measured at 190° C. and a load of 2.16 kg.

If necessary, the polyolefin-based resin may be a mixture of two or moretypes of polyolefin-based resins, or may be used in combination withother thermoplastic resins such as polystyrene and ionomer to the extentthat the properties of the polyolefin-based resin are not impaired.

The polyolefin-based resin used in the present invention can be obtainedusing catalysts such as a Ziegler catalyst, a metallocene catalyst, anda post-metallocene catalyst. The use of the Ziegler catalyst can providea polymer having a large Mw/Mn ratio. Moreover, when the polymersobtained using these catalysts are oxidatively decomposed with anorganic peroxide, the properties such as a molecular weight and a meltflow rate of the polymers can be adjusted.

Examples of the organic peroxide that may be used in the presentinvention include 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,t-butylperoxy laurate, 2,5-dimethyl-2,5-di(benzolyperoxy)hexane,t-butylperoxy benzoate, dicumyl peroxide,1,3-bis(t-butylperoxyisopropyl)benzene, and t-butylperoxyisopropylmonocarbonate.

The amount of the organic peroxide to be used is preferably 0.001 partsby weight to 0.1 parts by weight per 100 parts by weight of thepolyolefin-based resin. The oxidative decomposition of thepolyolefin-based resin can be performed, e.g., by heating and meltingthe polyolefin-based resin to which the organic peroxide has been addedin an extruder.

It is preferable that the polyolefin-based resin used in the presentinvention is not crosslinked. However, the polyolefin-based resin may becrosslinked by treatment with an organic peroxide or radiation.

The sterically hindered amine ether flame retardant used in the presentinvention is a compound expressed by the following general formula (1):

R¹NHCH₂CH₂CH₂NR²CH₂CH₂NR³CH₂CH₂CH₂NHR⁴  (1)

(where R¹, R² and one of R³ and R⁴ are an s-triazine moiety T expressedby the following general formula (2), the other of R³ and R⁴ is ahydrogen atom, and in the general formula (2), R⁵ is alkyl groups having1 to 12 carbon atoms such as methyl group, ethyl group, propyl group,butyl group, n-pentyl group, n-hexyl group, n-heptyl group, nonyl group,decyl group, undecyl group, dodecyl group, isopropyl group, isobutylgroup, sec-butyl group, tert-butyl group, 2-ethylbutyl group, isopentylgroup, 1-methylpentyl group, 1,3-dimethylbutyl group, 1-methylhexylgroup, isoheptyl group, 1,1,3,3-tetramethylpentyl group, 1-methylundecylgroup, and 1,1,3,3,5,5-hexamethylhexyl group, and R⁶ is a methyl group,a cyclohexyl group, or an octyl group).

Specific examples of the s-triazine moiety T expressed by the generalformula (2) include

-   2,4-bis[(1-methoxy-2,2,6,6-tetramethylpiperidine-4-yl)n-butylamino]-s-triazane,-   2,4-bis[(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidine-4-yl)n-butylamino]-s-triazine,-   and    2,4-bis[(1-octyloxy-2,2,6,6-tetramethylpiperidine-4-yl)n-butylamino]-s-triazine.

Specific examples of the sterically hindered amine ether flame retardantexpressed by the general formula (1) include

-   N,N′,N′″-tris{2,4-bis[(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidine-4-yl)n-butylamino]s-triazine-6-yl}-3,3′-ethylenediiminopropylamine,-   N,N′,N″-tris{2,4-bis[(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidine-4-yl)n-butylamino]-s-triazine-6-yl}-3,3′-ethylenediiminodipropylamine,-   N,N′,N″-tris{2,4-bis[(1-octyloxy-2,2,6,6-tetramethylpiperidine-4-yl)n-butylamino]-s-triazine-6-yl}-3,3′-ethylenediiminodipropylamine,-   N,N′,N′″-tris{2,4-bis[(1-octyloxy-2,2,6,6-tetramethylpiperidine-4-yl)n-butylamino]-s-triazine-6-yl}-3,3′-ethylenediiminopropylamine,-   N,N′,N′″-tris{2,4-bis[(1-methoxy-2,2,6,6-tetramethylpiperidine-4-yl)n-butylamino]-s-triazine-6-yl}-3,3′-ethylenediiminopropylamine,    and-   N,N′,N″-tris{2,4-bis[(1-methoxy-2,2,6,6-tetramethylpiperidine-1′-yl)n-butylamino]-s-triazine-6-yl}-3,3′-ethylenediiminopropylamine.    They may be used individually or in combination of two or more.

The amount of the sterically hindered amine ether flame retardant usedin the present invention is preferably 0.01 parts by weight to 20 partsby weight, more preferably 0.02 parts by weight to 10 parts by weight,and even more preferably 0.05 parts by weight to 5 parts by weight per100 parts by weight of the polyolefin-based resin. If the amount of theflame retardant is less than 0.01 parts by weight, sufficient flameresistance may not be achieved. If the amount of the flame retardant ismore than 20 parts by weight, it is likely that the mechanical strengthis reduced, and the in-mold expansion moldability is deteriorated(particularly the deterioration of the surface appearance) because thecell diameter is finer. Thus, the cost is increased, which results in aneconomic disadvantage.

In the present invention, the sterically hindered amine ether flameretardant may be added to the polyolefin-based resin either directly orindirectly. In an indirect method, a polyolefin-based resin masterbatchcontaining, e.g., 5 wt % to 50 wt % of the sterically hindered amineether flame retardant is prepared, and then added to thepolyolefin-based resin. For ease of addition, the indirect method ispreferred.

The present invention uses the sterically hindered amine ether flameretardant in combination with the phosphoric ester, and thus can achieveexcellent flame retardant performance compared to the conventionaltechniques even in the case of an in-mold expansion molded articlehaving a higher density or a larger thickness.

Examples of the phosphoric ester used in the present invention includethe following: aliphatic phosphoric esters such as trimethyl phosphate,triethyl phosphate, triisopropyl phosphate, trineopentyl phosphate,tri-tert-butyl phosphate, tributoxyethyl phosphate, triisobutylphosphate, and tri(2-ethylhexyl)phosphate; aromatic phosphoric esterssuch as triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate,cresyl diphenyl phosphate, tert-butylphenyl diphenyl phosphate,bis-(tert-butylphenyl)phenyl phosphate,tris-(tert-butylphenyl)phosphate, isopropylphenyl diphenyl phosphate,bis-(isopropylphenyl)diphenyl phosphate,tris-(isopropylphenyl)phosphate, cresyl diphenyl phosphate, andcresyldi-2,6-dixylenyl phosphate; and a phosphoric ester having botharomatic and aliphatic hydrocarbon groups in a molecule such as2-ethylhexyl diphenyl phosphate. In the following, the aromaticphosphoric ester along with the phosphoric ester having both aromaticand aliphatic hydrocarbon groups in a molecule may be referred to as“aromatic-based phosphoric ester”. These phosphoric esters may be usedindividually or in combination of two or more.

The phosphoric ester used in the present invention is not particularlylimited as long as it can withstand extrusion kneading and decompositionin an aqueous dispersion medium. In terms of the volatility, thephosphoric ester having a molecular weight of 300 or more is preferred.Moreover, in terms of the dispersibility in the polyolefin-based resin,the high temperature stability, the volatility, or the like, thephosphoric ester is preferably the aromatic-based phosphoric ester, morepreferably the aromatic phosphoric ester, and even more preferably acondensed phosphoric ester containing at least two phosphate sites ofthe aromatic phosphoric ester in a molecule.

Specific examples of the condensed phosphoric ester used in the presentinvention have structures expressed by the following general formulas(3) and (4), and can be suitably used.

In terms of the volatility, the hydrolysis resistance, or the like, itis more preferable that the aromatic phosphoric ester has an alkyl groupon the benzene ring of the aromatic hydrocarbon radical. Examples of thealkyl group include methyl group, ethyl group, propyl group, butylgroup, n-pentyl group, n-hexyl group, n-heptyl group, nonyl group, decylgroup, undecyl group, dodecyl group, isopropyl group, isobutyl group,sec-butyl group, tert-butyl group, 2-ethylbutyl group, isopentyl group,1-methylpentyl group, 1,3-dimethylbutyl group, 1-methylhexyl group,isoheptyl group, 1,1,3,3-tetramethylpentyl group, 1-methylundecyl group,and 1,1,3,3,5,5-hexamethylhexyl group.

The present invention uses the phosphoric ester that is easilyhydrolyzed as the flame retardant. In general, a system using thephosphoric ester is required to eliminate moisture as much as possibleto suppress a reduction in flame resistance due to hydrolysis.Surprisingly, however, the present invention can achieve stable flameresistance even if the polyolefin-based resin particles including thephosphoric ester that is easily hydrolyzed are heated under pressure inthe aqueous dispersion medium. This is because the expansion temperaturecan be kept low by expansion under reduced pressure, which is anexpansion process of the present invention, even if the polyolefin-basedresin particles including the phosphoric ester are heated under pressurein the aqueous dispersion medium. In the expansion under reducedpressure, the polyolefin-based resin particles can be generally expandedat about 100° C. to 160° C., although the temperature depends on themelting point of the polypropylene-based resin used, and therefore it isconsidered that the phosphoric ester is not likely to be hydrolyzed evenby heating under pressure in the aqueous dispersion medium.

The amount of the phosphoric ester used in the present invention ispreferably 0.01 parts by weight to 10 parts by weight, more preferably0.02 parts by weight to 5 parts by weight, and even more preferably 0.03parts by weight to 3 parts by weight per 100 parts by weight of thepolyolefin-based resin. If the amount of the phosphoric ester is lessthan 0.01 parts by weight, sufficient flame resistance may not beachieved. If the amount of the phosphoric ester is more than 10 parts byweight, it is likely that the mechanical strength is reduced, and thein-mold expansion moldability is deteriorated (such as particularly thedeterioration of the surface appearance and the increase of thedimensional shrinkage) because the cell diameter is finer. Thus, thecost is increased, which results in an economic disadvantage.

The phosphoric ester may be added to the polyolefin-based resin eitherdirectly or indirectly. In an indirect method, a polyolefin-based resinmasterbatch containing, e.g., 5 wt % to 50 wt % of the phosphoric esteris prepared, and then added to the polyolefin-based resin. For ease ofaddition, the indirect method is preferred.

In the present invention, flame retardants and flame retardant aidsother than the above flame retardants may be further added as needed.Examples of the additional flame retardant and flame retardant aidinclude the following: phosphorus-containing compounds having aphosphorus atom in a molecule such as red phosphorus, a phosphorusoxide, a phosphoric acid compound, phosphates, phosphazenes, aminephosphates, amide phosphates, a trivalent aliphatic phosphorus compound,and a trivalent aromatic phosphorus compound; nitrogen-containingcompounds having a nitrogen atom in a molecule such as a cyanuric acidor an isocyanuric acid and a derivative thereof, salts of a cyanuricacid or an isocyanuric acid and a derivative thereof, a compound havinga triazine skeleton, an azo compound, tetrazole amine salts, tetrazolemetal salts, and a tetrazole compound; boron compounds having a boronatom in a molecule such as a boric acid compound, borates, hydrates ofthe boric acid compound and the borates, derivatives of the boric acidcompound, the borates, and the hydrates, and boron oxides; halogencompounds having a halogen atom (e.g., chlorine, bromine, or fluorine)in a molecule such as halogenated aliphatic compounds and derivativesthereof, halogenated aromatic compounds and derivatives thereof,halogenated bisphenols and derivatives thereof, a halogenated bisphenolderivative oligomer, a halogenated acrylic resin, a halogenated epoxyresin, a halogenated polystyrene resin, chlorinated paraffin, andpolytetrafluoroethylene; a compound that is formed by combining theabove flame retardants and has at least two types of phosphorus,nitrogen, boron, and halogen atoms in a molecule; inorganic flameretardants such as a metal hydroxide and a metal oxide; an antimonytrioxide; carbon black; a polyhydric alcohol; and glycols.

In the present invention, any of the following additives may be added asneed to the polyolefin-based resin to the extent that the effect of thepresent invention is not impaired, thereby providing a polyolefin-basedresin composition. Examples of the additives include a nucleating agentsuch as talc, stabilizers such as an antioxidant, a metal deactivator, aphosphorus-based processing stabilizer; an ultraviolet absorber, anultraviolet stabilizer, a fluorescent brightener, and a metal soap, across-linking agent, a chain transfer agent, a lubricant, a plasticizer,a filler, a reinforcing agent, an inorganic pigment, an organic pigment,a conductivity improving agent, a flame resistance improving agent, anda surface-active or polymeric antistatic agent.

For ease of pre-expansion of the polyolefin-based resin composition, ingeneral, the polyolefin-based resin is melted and mixed with thesterically hindered amine ether flame retardant, the phosphoric ester,and optionally the above additives in advance by using an extruder, akneader, a Banbury mixer, a roller, or the like. Then, the resultantmixture is formed into polyolefin-based resin particles having a desiredparticle shape such as a cylinder, an ellipse, a sphere, a cube, or arectangular parallelepiped. The average particle weight of thepolyolefin-based resin particles is preferably 0.5 mg to 3.0 mg, andmore preferably 0.5 mg to 2.0 mg.

The method for producing the polyolefin-based resin pre-expandedparticles of the present invention is not particularly limited, andso-called expansion under reduced pressure is preferred. In this method,the polyolefin-based resin particles are dispersed in a dispersionmedium with a dispersing agent or the like in the presence of a blowingagent in a closed container, and heated to a predetermined expansiontemperature under pressure so that the resin particles are impregnatedwith the blowing agent. Thereafter, the dispersion in the closedcontainer is released into a low pressure region and thepolyolefin-based resin particles are expanded, while the temperature andthe pressure in the container are maintained constant.

The heating temperature in the closed container is preferably in therange of (the melting point of the polyolefin-based resin particles−25°C.) to (the melting point of the polyolefin-based resin particles+25°C.), and more preferably in the range of (the melting point of thepolyolefin-based resin particles−15° C.) to (the melting point of thepolyolefin-based resin particles+15° C.). By heating thepolyolefin-based resin particles to this temperature under pressure, thepolyolefin-based resin particles are impregnated with the blowing agent.Thereafter, one end of the closed container is opened so that thepolyolefin-based resin particles are released into the atmosphere wherethe pressure is lower than that in the closed container. Thus, thepolyolefin-based resin pre-expanded particles can be produced.

The closed container in which the polyolefin-based resin particles aredispersed is not particularly limited as long as it can withstand thepressure and the temperature during the production of thepolyolefin-based resin pre-expanded particles. The closed container canbe, e.g., an autoclave.

The dispersion medium can be, e.g., methanol, ethanol, ethylene glycol,glycerin, or water. In particular, water is preferred.

It is preferable that a dispersing agent is used in the dispersionmedium to prevent coalescence of the polyolefin-based resin particles.Examples of the dispersing agent include inorganic dispersing agentssuch as tribasic calcium phosphate, magnesium phosphate, basic magnesiumcarbonate, calcium carbonate, barium sulfate, kaoline, talc, and clay.

Moreover, a dispersing aid may be used as needed. Examples of thedispersing aid include sodium dodecylbenzenesulfonate, sodiumn-paraffinsulfonate, sodium α-olefinsulfonate, magnesium sulfate,magnesium nitrate, magnesium chloride, aluminum sulfate, aluminumnitrate, aluminum chloride, iron sulfate, iron nitrate, and ironchloride. In particular, the tribasic calcium phosphate and the sodiumn-paraffinsulfonate are preferably used in combination.

The amounts of the dispersing agent and the dispersing aid varydepending on the types thereof and the type and amount of thepolyolefin-based resin used. In general, the amount of the dispersingagent is preferably 0.2 parts by weight to 3 parts by weight per 100parts by weight of the dispersion medium, and the amount of thedispersing aid is preferably 0.001 parts by weight to 0.1 parts byweight per 100 parts by weight of the dispersion medium. By controllingthe amounts of the dispersing agent and the dispersing aid in the aboveranges, the dispersion stability can be ensured, and the dispersingagent is not likely to be attached to the surfaces of the pre-expandedparticles. Accordingly, the fusion of the pre-expanded particles may notbe impaired during in-mold expansion molding.

In general, the polyolefin-based resin particles are preferably used inan amount of 20 parts by weight to 100 parts by weight per 100 parts byweight of the dispersion medium so as to ensure good dispersibility inthe dispersion medium.

The present invention uses the sterically hindered amine ether flameretardant in combination with the phosphoric ester, and thus can reducethe amount of the dispersing agent attached to the pre-expandedparticles compared to the conventional techniques. If a large amount ofthe dispersing agent is attached to the pre-expanded particles, thefusion of the pre-expanded particles may be impaired during in-moldexpansion molding. The general production of the pre-expanded particlesrequires a washing process of the pre-expanded particles to reduce theamount of the dispersing agent attached to the pre-expanded particles.However, according to the amount of the dispersing agent attached to thepre-expanded particles of the present invention, the washing time can beshortened, and the use of the agent and the solvent also can be reduced,thereby reducing the environmental load and the cost.

In the production of the polyolefin-based resin pre-expanded particles,the blowing agent is not particularly limited. Examples of the blowingagent include aliphatic hydrocarbons such as propane, isobutane, normalbutane, isopentane, and normal pentane, inorganic gas such as air,nitrogen, and carbon dioxide, water, and a mixture of these materials.The amount of the blowing agent varies depending on the resin used, theblowing agent, and the desired expansion ratio, and may be appropriatelydetermined in accordance with the desired expansion ratio of thepolyolefin-based resin pre-expanded particles. In general, the amount ofthe blowing agent is preferably 1 part by weight to 60 parts by weightper 100 parts by weight of the polyolefin-based resin particles.

As the blowing agent used in the present invention, the aliphatichydrocarbons such as isobutane and normal butane and carbon dioxide areparticularly preferred. Since these blowing agents accelerate theplasticization of the polyolefin-based resin, the polyolefin-based resinparticles can be expanded at a lower pressure and a lower temperaturecompared to the case of using only water, air, or nitrogen as theblowing agent. Consequently, the hydrolysis of the phosphoric ester canbe further suppressed, and more stable flame resistance can be achieved.

When water is used as the blowing agent, it is preferable that at leastone compound selected from a hydrophilic polymer, a polyhydric alcohol,and a compound having a triazine skeleton is added to thepolyolefin-based resin particles in order to provide thepolyolefin-based resin pre-expanded particles with a high expansionratio.

Examples of the hydrophilic polymer include carboxyl group containingpolymers such as an ethylene-acrylic acid-maleic anhydride ternarycopolymer, an ethylene-(meth)acrylic acid copolymer, and an ionomerresin obtained by crosslinking an ethylene-(meth)acrylic acid copolymerwith a metal ion, and polyethylene glycol. They may be used individuallyor in combination of two or more.

The amount of the hydrophilic polymer depends on the type of thehydrophilic polymer and is not particularly limited. In general, theamount of the hydrophilic polymer is preferably 0.01 parts by weight to20 parts by weight, and more preferably 0.1 parts by weight to 5 partsby weight per 100 parts by weight of the polyolefin-based resinparticles. If the amount of the hydrophilic polymer is less than 0.01parts by weight, it may be difficult to provide the polyolefin-basedresin pre-expanded particles with a high expansion ratio. If the amountof the hydrophilic polymer is more than 20 parts by weight, the heatresistance and the mechanical strength can be significantly reduced.

Examples of the polyhydric alcohol include ethylene glycol, glycerin,erythritol, and pentaerythritol. They may be used individually or incombination of two or more.

The amount of the polyhydric alcohol depends on the type of thepolyhydric alcohol and is not particularly limited. In general, theamount of the polyhydric, alcohol is preferably 0.01 parts by weight to10 parts by weight, and more preferably 0.1 parts by weight to 2 partsby weight per 100 parts by weight of the polyolefin-based resinparticles. If the amount of the polyhydric alcohol is less than 0.01parts by weight, it may be difficult to provide the polyolefin-basedresin pre-expanded particles with a high expansion ratio. If the amountof the polyhydric alcohol is more than 10 parts by weight, the heatresistance and the mechanical strength can be significantly reduced.

The preferred compound having a triazine skeleton has a molecular weightof 300 or less per unit triazine skeleton. In this case, the molecularweight per unit triazine skeleton is a value obtained by dividing themolecular weight by the number of triazine skeletons contained in amolecule. If the molecular weight per unit triazine skeleton is morethan 300, a variation in expansion ratio and a variation in celldiameter may be considerable. Examples of the compound having amolecular weight of 300 or less per unit triazine skeleton includemelamine (chemical name: 1,3,5-triazine-2,4,6-triamine), ammeline(chemical name: 1,3,5-triazine-2-hydroxy-4,6-diamine), ammelide(chemical name: 1,3,5-triazine-2,4-hydroxy-6-amine), cyanuric acid(chemical name: 1,3,5-triazine-2,4,6-triol), tris(methyl)cyanurate,tris(ethyl)cyanurate, tris(butyl)cyanurate,tris(2-hydroxyethyl)cyanurate, and melamine-isocyanuric acidcondensation product. They may be used individually or in combination oftwo or more. Among them, the melamine, the isocyanuric acid, and themelamine-isocyanuric acid condensation product are preferred so as toprovide the polyolefin-based resin pre-expanded particles with a highexpansion ratio by reducing the variation in expansion ratio and thevariation in cell diameter.

The amount of the compound having a triazine skeleton depends on thetype of the compound having a triazine skeleton and is not particularlylimited. In general, the amount of the compound having a triazineskeleton is preferably 0.01 parts by weight to 15 parts by weight, andmore preferably 0.1 parts by weight to 3 parts by weight per 100 partsby weight of the polyolefin-based resin particles. If the amount of thecompound having a triazine skeleton is less than 0.01 parts by weight,it may be difficult to provide the polyolefin-based resin pre-expandedparticles with a high expansion ratio. If the amount of the compoundhaving a triazine skeleton is more than 15 parts by weight, the heatresistance and the mechanical strength can be significantly reduced.

When the carbon dioxide is used as the blowing agent, borax, zincborate, glycerin, and low molecular weight hydrophilic materials such aspolyethylene glycol having a molecular weight of 300 or less can beadded to the polyolefin-based resin, thereby providing thepolyolefin-based resin pre-expanded particles with a high expansionratio and a uniform cell diameter.

The expansion ratio of the polyolefin-based resin pre-expanded particlesobtained by the above production method is preferably 5 times to 50times, and more preferably 7 times to 45 times.

The polyolefin-based resin pre-expanded particles with a higherexpansion ratio may be produced, e.g., by a two-stage expansion process.In the two-stage expansion process, first, polyolefin-based resinpre-expanded particles with an expansion ratio of 5 times to 35 timesare produced. Then, the polyolefin-based resin pre-expanded particlesare placed in a closed container and pressurized so that nitrogen, air,or the like is impregnated into the pre-expanded particles, and thus thepressure inside the pre-expanded particles becomes higher than thenormal pressure. Subsequently, the polyolefin-based resin pre-expandedparticles are further expanded by heating with steam or the like.

The expansion ratio is determined in the following manner. The weight w(g) of the polyolefin-based resin pre-expanded particles and the volumev (cm³) of the polyolefin-based resin pre-expanded particles immersed inethanol are measured. Then, the expansion ratio is calculated byfollowing equation, where d (g/cm³) represents the density of thepolyolefin-based resin particles before expansion.

Expansion ratio=d×v/w

The average cell diameter of the polyolefin-based resin pre-expandedparticles of the present invention is preferably 50 μm to 800 μm, andmore preferably 100 μm to 600 μm. The average cell diameter isdetermined in the following manner. Thirty pre-expanded particles arerandomly taken out of the polyolefin-based resin pre-expanded particles,and the cell diameters are measured in accordance with JIS K6402. Thus,the average cell diameter is calculated.

The closed cell ratio of the polyolefin-based resin pre-expandedparticles of the present invention is preferably 88% or more, and morepreferably 93% or more. The closed cell ratio is determined in thefollowing manner. The volume of the closed cells of the polyolefin-basedresin pre-expanded particles is measured with an air comparisonpycnometer. On the other hand, the apparent volume of thepolyolefin-based resin pre-expanded particles is determined by anethanol immersion method. The closed cell ratio is calculated bydividing the closed cell volume by the apparent volume.

In the differential scanning calorimetry of the polyolefin-based resinpre-expanded particles of the present invention, it is preferable that aDSC curve obtained when the temperature of 5 to 6 mg of thepolyolefin-based resin pre-expanded particles is increased from 40° C.to 220° C. at a rate of 10° C./min has two melting peaks.

The DSC ratio of the polyolefin-based resin pre-expanded particles ofthe present invention is preferably 13% to 50%, and more preferably 18%to 40%. If the DSC ratio is within this range, the polyolefin-basedresin in-mold expansion molded article is likely to have anaesthetically pleasing surface. The DSC ratio is determined in thefollowing manner. Tangent lines are drawn from a point on the DSC curvewhere the endothermic amount is the smallest between the two meltingpeaks to the DSC curve on the low temperature side and the hightemperature side, respectively. The low-temperature area enclosed by theDSC curve and the tangent line extending to the low temperature side isdefined as a heat quantity Ql of the melting peak on the low temperatureside. The high-temperature area enclosed by the DSC curve and thetangent line extending to the high temperature side is defined as a heatquantity Qh of the melting peak on the high temperature side. The DSCratio is a ratio of the melting peak on the high temperature side[Qh/(Ql+Qh)×100] calculated from the heat quantities Ql and Qh.

The polyolefin-based resin pre-expanded particles of the presentinvention can be formed into a polyolefin-based resin in-mold expansionmolded article by in-mold expansion molding.

The in-mold expansion molding of the polyolefin-based resin pre-expandedparticles of the present invention may be performed by conventionallyknown methods, e.g., a) using the polyolefin-based resin pre-expandedparticles as they are, b) impregnating inorganic gas such as air intothe pre-expanded particles to impart expandability to them in advance,or c) filling the pre-expanded particles in a compressed state into amold.

A specific method for forming a polyolefin-based resin in-mold expansionmolded article from the polyolefin-based resin pre-expanded particles ofthe present invention can be as follows. For example, thepolyolefin-based resin pre-expanded particles are placed in a pressurevessel and pressurized by air in advance, so that the air is impregnatedinto the pre-expanded particles to impart expandability to them. Theresultant pre-expanded particles are filled into a molding space that isprovided between two molds, and can be closed but not hermeticallysealed. Then, the pre-expanded particles are heated with steam or thelike (as a heating medium) at a steam pressure of about 0.10 to 0.4 MPa(G) for about 3 to 30 seconds, and thus molded and fused together.Subsequently, the molds are cooled, e.g., by water cooling and opened,thereby providing the polyolefin-based resin in-mold expansion moldedarticle.

The density of the polyolefin-based resin in-mold expansion moldedarticle obtained from the polyolefin-based resin pre-expanded particlesof the present invention is preferably 10 kg/m³ to 300 kg/m³, and morepreferably 15 kg/m³ to 250 kg/m³, and even more preferably 15 kg/m³ to150 kg/m³.

When the polyolefin-based resin in-mold expansion molded article of thepresent invention is tested in accordance with the UL94 horizontalburning test for foamed materials (UL94 HF), it can meet HF-2 in a widerrange of thickness and density than a conventional molded article.

EXAMPLES

Next, the present invention will be described based on Examples andComparative Examples. However, the present invention is not limited tothe following Examples.

In Examples and Comparative Examples, the following materials were usedwithout any particular treatment such as purification.

-   -   Polyolefin-based resin:ethylene-propylene random copolymer [with        an ethylene content of 2.8%, a MFR of 6.0 g/10 min, and a        melting point of 145° C.]    -   Sterically hindered amine ether flame retardant [FLAMESTAB NOR        116 produced by Ciba Japan Ltd. (BASF Japan Ltd.); general        formula (5)]    -   Phosphoric ester [PX-200 (molecular weight: 687, P %:9.0%)        produced by DAIHACHI CHEMICAL INDUSTRY CO., LTD.; general        formula (3)]    -   Ammonium polyphosphate [produced by SUZUHIRO CHEMICAL CO., LTD.]    -   Magnesium hydroxide [produced by Kyowa Chemical Industry CO.,        Ltd.]    -   Carbon black [produced by SUMIKA COLOR CO., LTD.]    -   Powdery tribasic calcium phosphate [produced by TAIHEI CHEMICAL        INDUSTRIAL CO., LTD.]    -   Sodium n-paraffinsulfonate [LATEMUL PS produced by Kao        Corporation]

The evaluations of Examples and Comparative Examples were performed inthe following manner.

(DSC Ratio)

Using a differential scanning calorimeter, the temperature of 5 to 6 mgof the polyolefin-based resin pre-expanded particles was increased from40° C. to 220° C. at a rate of 10° C./min, so that a DSC curve (seeFIG. 1) was obtained. The DSC curve had two melting peaks, and the DSCratio was calculated by the following equation, where Ql represents theheat quantity of the melting peak on the low temperature side and Qhrepresents the heat quantity of the melting peak on the high temperatureside.

DSC ratio=Qh/(Ql+Qh)×100

(Expansion Ratio)

The weight w (g) of the polyolefin-based resin pre-expanded particlesand the volume v (cm³) of the polyolefin-based resin pre-expandedparticles immersed in ethanol were measured. Then, the expansion ratiowas calculated by the following equation, where d (g/cm³) represents thedensity of the polyolefin-based resin particles before expansion.

Expansion ratio=d×v/w

(Average Cell Diameter)

Thirty pre-expanded particles were randomly taken out of thepolyolefin-based resin pre-expanded particles produced, and the celldiameters were measured in accordance with JIS K6402. Thus, the averagecell diameter was calculated.

(Closed Cell Ratio)

The volume of the closed cells of the polyolefin-based resinpre-expanded particles produced was measured with an air comparisonpycnometer (Model 930 manufactured by Beckman Coulter, Inc.). On theother hand, the apparent volume of the polyolefin-based resinpre-expanded particles was determined by an ethanol immersion method.The closed cell ratio was calculated by dividing the dosed cell volumeby the apparent volume.

(Amount of Dispersing Agent Attached to Pre-Expanded Particles)

The polyolefin-based resin pre-expanded particles were washed withrunning water for 30 seconds, and then dried in an oven at 60° C. for 24hours. Immediately after being taken out of the oven, the pre-expandedparticles were allowed to stand in a thermo-hygrostat at 23° C. and 50%RH for 72 hours. Next, in the thermo-hygrostat, about 100 g of thepre-expanded particles were accurately weighed to the third decimalplace, and the weight of the pre-expanded particles to which thedispersing agent was attached was represented by F (g). Thereafter, thetotal amount of the pre-expanded particles thus weighed was immersed in5 L of 1N hydrochloric acid solution for 10 minutes, then immersed in 5L of ion-exchanged water for 1 minute to wash off the hydrochloric acidsolution, and further immersed in 5 L of 1N sodium hydroxide solutionfor 10 minutes. A series of the operations was repeated twice, and thetotal amount of the resultant pre-expanded particles was dried in anoven at 60° C. for 24 hours. Immediately after being taken out of theoven, the pre-expanded particles were allowed to stand in athermo-hygrostat at 23° C. and 50% RH for 72 hours. Next, in thethermo-hygrostat; the pre-expanded particles were accurately weighed tothe third decimal place, and the weight of the pre-expanded particlesafter acid and alkali washing was represented by S (g). The differencebetween the weight F (g) after water washing and the weight S (g) afteracid and alkali washing was calculated by the following equation as anamount of the dispersing agent attached to the surfaces of thepre-expanded particles.

Amount of dispersing agent attached to pre-expanded particles(ppm)=(F−S)/F×10⁶

(Surface Appearance)

The surface of the in-mold expansion molded article was visuallyobserved and evaluated based on the following criteria.

◯: The surface was free from unevenness, and there was almost no voidbetween the particles.

X: The surface was uneven, and there was a very large void between theparticles.

(Fusion)

The in-mold expansion molded article produced was fractured, and thecross section was observed. Then, the proportion of the number of brokenparticles to the total number of particles present at the cross sectionwas determined and evaluated based on the following criteria.

◯: The proportion of the broken particles was 60% or more.

X: The proportion of the broken particles was less than 60%.

(Molded Article Density)

The in-mold expansion molded article produced was cut to a length of 150mm, a width of 50 mm, and an intended thickness as a burning testsample. The weight w (g) of the sample was measured, and the volume v(cm³) was obtained from the length, the width, and the thickness of thesample. The molded article density was calculated by the followingequation.

Molded article density=w/v(g/cm³)

The burning test samples having the above dimensions (thickness: 3.5 mm,7 mm, 13 mm) were tested in accordance with UL94 HF and evaluated basedon the following criteria.

Afterflame time: The period of time between when the fire of a gasburner was extinguished and when the fire of each of the samples wasextinguished was defined as an afterflame time, and the average of theafterflame times of five tests was calculated. The flame retardantperformance is higher as the afterflame time is shorter.

Examples 1 to 5

[Production of Resin Particles]

100 parts by weight of a polyolefin-based resin (i.e., anethylene-propylene random copolymer with an ethylene content of 2.8%, aMFR of 6.0 g/10 min, and a melting point of 145° C.) were mixed with0.01 parts by weight of talc as a nucleating agent, a phosphoric ester(PX-200 (molecular weight: 687, P %:9.0%) produced by DAIHACHI CHEMICALINDUSTRY CO., LTD.) expressed by the general formula (3):

at a compounding ratio shown in Table 1, a compound (FLAMESTAB NOR. 116produced by Ciba Japan Ltd. (BASF Japan Ltd.)) expressed by thefollowing general formula (5):

RNHCH₂CH₂CH₂NRCH₂CH₂NHCH₂CH₂CH₂NHR  (5)

(where R is an s-triazine moiety T expressed by the following generalformula (6))

at a compounding ratio shown in Table 1, and a carbon black (40%masterbatch) at a compounding ratio shown in Table 1. The mixture waskneaded by a 50 mm φ single screw extruder, and then granulated intopolyolefin-based resin particles (1.2 mg/grain).

[Production of Pre-Expanded Particles]

A 10 L closed container was charged with 100 parts by weight of theresin particles thus produced, 10 parts by weight of isobutane, 300parts by weight of water, 1.6 parts by weight of powdery tribasiccalcium phosphate, and 0.03 parts by weight of sodiumn-paraffinsulfonate, and the inside of the closed container was heatedto an expansion temperature shown in Table 1. Then, the pressure in thecontainer was adjusted to a predetermined expansion pressure shown inTable 1 by injecting isobutane into the container. Subsequently, whilethe pressure in the container was maintained with nitrogen, a valveprovided on the lower portion of the closed container was opened so thatthe aqueous dispersion was released into the atmosphere through anorifice plate having openings of 4.0 mm φ diameter, thereby providingpolyolefin-based resin pre-expanded particles. The polyolefin-basedresin pre-expanded particles were evaluated as described above. Table 2shows the results.

[Production of in-Mold Expansion Molded Article]

Next, the polyolefin-based resin pre-expanded particles thus producedwere washed with 0.1N hydrochloric acid solution. Moreover, thepre-expanded particles were placed in a pressure vessel and pressurizedby air at an internal pressure of 0.18 to 0.23 MPa. Then, thepre-expanded particles were filled into a mold of 400 mm×300 mm×22 mm,heated with steam at 0.28 MPa (G) for 10 seconds, and fused together toform a polyolefin-based resin in-mold expansion molded article. Withrespect to the in-mold expansion molded article thus produced, thesurface appearance, the fusion rate, the molded article density, and theburning test were evaluated. Table 2 shows the results.

Comparative Examples 1 to 5

[Production of Resin Particles]

The compounds expressed by the general formulas (3) and (5) used inExamples, various flame retardants (magnesium hydroxide and ammoniumpolyphosphate), and carbon black were added at their respective ratiosshown in Table 1, and thus resin particles were produced in the samemanner as Examples.

[Production of Pre-Expanded Particles]

Polyolefin-based resin pre-expanded particles were produced in the samemanner as Examples except that the expansion temperature and theexpansion pressure were changed to the conditions shown in Table 2. Thepolyolefin-based resin pre-expanded particles were evaluated asdescribed above. Table 2 shows the results.

[Production of in-Mold Expansion Molded Article]

A polyolefin-based resin in-mold expansion molded article was producedin the same manner as Examples. With respect to the in-mold expansionmolded article thus produced, the surface appearance, the fusion rate,the molded article density, and the burning test were evaluated. Table 2shows the results.

TABLE 1 Sterically Phosphoric hindered amine Magnesium Carbon Meltingpoint of ester ether flame Ammonium hydroxide black polyolefin-basedExpansion Expansion (parts by retardant polyphosphate (parts by (partsby resin temperature pressure weight) (parts by weight) (parts byweight) weight) weight) (° C.) (° C.) (MPa) Example 1 1.0 2.0 0.0 0.00.3 143.2 146.1 1.37 Example 2 1.0 2.0 0.0 0.0 0.3 143.2 146.4 1.38Example 3 1.0 2.0 0.0 0.0 0.3 143.2 146.5 1.40 Example 4 3.0 2.0 0.0 0.00.3 142.6 145.6 1.39 Example 5 0.5 2.0 0.0 0.0 0.3 143.8 146.5 1.38Comparative 0.0 2.0 0.0 0.0 0.3 144.1 146.8 1.36 Example 1 Comparative0.0 2.0 0.0 0.0 0.3 144.1 146.7 1.39 Example 2 Comparative 0.0 2.0 1.00.0 0.3 144.2 147.5 1.20 Example 3 Comparative 0.0 2.0 0.0 15.0 0.3143.2 147.1 1.27 Example 4 Comparative 1.0 0.0 0.0 0.0 0.3 143.8 146.71.39 Example 5

TABLE 2 Pre-expanded particles Amount of In-mold expansion moldedarticle Average dispersing Molded Flame resistance evaluation cellClosed agent article (afterflame time/sec) DSC Expansion diameter cellratio attached Surface density Sample thickness ratio (%) ratio (μm) (%)(ppm) appearance Fusion (g/cm³) 3.5 mm 7 mm 13 mm Example 1 27.1 9.1 22399.7 1080 ◯ ◯ 0.071 0 0 10 Example 2 26.1 11.3 215 99.6 1110 ◯ ◯ 0.060 00 4 Example 3 20.3 14.1 247 99.6 1180 ◯ ◯ 0.045 0 0 0 Example 4 23.013.2 230 99.1 980 ◯ ◯ 0.051 0 0 0 Example 5 22.8 13.4 218 99.7 1200 ◯ ◯0.050 0 0 1 Comparative 28.4 11.1 211 99.6 1580 ◯ ◯ 0.060 0 21 50Example 1 Comparative 28.1 14.2 228 99.8 1620 ◯ ◯ 0.046 0 5 28 Example 2Comparative 28.6 14.4 210 97.1 520 X ◯ 0.045 0 4 30 Example 3Comparative 26.7 13.8 121 98.8 3200 ◯ X 0.048 20 39 88 Example 4Comparative 25.2 12.8 260 99.6 1200 ◯ ◯ 0.053 31 70 129 Example 5

Examples 1 to 5 using the sterically hindered amine ether flameretardant in combination with the phosphoric ester showed good flameretardant performance compared to Comparative Example 1 to 2 using thesterically hindered amine ether flame retardant alone and ComparativeExample 5 using the phosphoric ester alone. In Comparative Examples 3 to4 using the sterically hindered amine ether flame retardant and themagnesium hydroxide or the ammonium polyphosphate, a favorable in-moldexpansion molded article was not produced, and the flame retardantperformance was not improved.

Moreover, the amount of dispersing agent attached to the pre-expandedparticles was smaller in Examples 1 to 5 using the sterically hinderedamine ether flame retardant in combination with the phosphoric esterthan in Comparative Examples 1 to 2 using no phosphoric ester. Thus, itcan be expected that the washing process will be shortened, and also theamount of the agent will be reduced.

INDUSTRIAL APPLICABILITY

The use of the polyolefin-based resin pre-expanded particles of thepresent invention can provide an in-mold expansion molded article thathas excellent flame resistance compared to the conventional expansionmolded article even in the case of a sample having a higher density or alarger thickness while maintaining good in-mold expansion moldabilityand surface appearance that are comparable to those of a conventionalexpansion molded article.

1. Polyolefin-based resin pre-expanded particles comprising apolyolefin-based resin composition including: a polyolefin-based resin;a sterically hindered amine ether flame retardant expressed by thefollowing general formula (1):R¹NHCH₂CH₂CH₂NR²CH₂CH₂NR³CH₂CH₂CH₂NHR⁴  (1) (where R¹, R² and one of R³and R⁴ are an s-triazine moiety T expressed by the following generalformula (2):

the other of R³ and R⁴ is a hydrogen atom, and in the general formula(2), R⁵ is an alkyl group having 1 to 12 carbon atoms and R⁶ is a methylgroup, a cyclohexyl group, or an octyl group); and a phosphoric ester.2. The polyolefin-based resin pre-expanded particles according to claim1, obtained by dispersing polyolefin-based resin particles composed ofthe polyolefin-based resin composition into an aqueous dispersion mediumin a presence of a blowing agent, heating the dispersion thus obtainedunder pressure, and releasing the dispersion into a low pressure region.3. The polyolefin-based resin pre-expanded particles according to claim1, wherein the phosphoric ester is an aromatic-based phosphoric ester.4. The polyolefin-based resin pre-expanded particles according to claim2, wherein the blowing agent is at least one selected from the groupconsisting of isobutane and normal butane.
 5. The polyolefin-based resinpre-expanded particles according to claim 2, wherein the blowing agentis carbon dioxide.
 6. The polyolefin-based resin pre-expanded particlesaccording to claim 1, wherein the polyolefin-based resin compositionincludes 0.01 parts by weight to 20 parts by weight of the stericallyhindered amine ether flame retardant expressed by the general formula(1) and 0.01 parts by weight to 10 parts by weight of the phosphoricester with respect to 100 parts by weight of the polyolefin-based resin.7. The polyolefin-based resin pre-expanded particles according to claim1, wherein the polyolefin-based resin is a polypropylene-based resin. 8.A polyolefin-based resin in-mold expansion molded article produced byin-mold expansion molding of the polyolefin-based resin pre-expandedparticles according to claim
 1. 9. The polyolefin-based resinpre-expanded particles according to claim 2, wherein the phosphoricester is an aromatic-based phosphoric ester.
 10. The polyolefin-basedresin pre-expanded particles according to claim 2, wherein thepolyolefin-based resin composition includes 0.01 parts by weight to 20parts by weight of the sterically hindered amine ether flame retardantexpressed by the general formula (1) and 0.01 parts by weight to 10parts by weight of the phosphoric ester with respect to 100 parts byweight of the polyolefin-based resin.
 11. The polyolefin-based resinpre-expanded particles according to claim 2, wherein thepolyolefin-based resin is a polypropylene-based resin.
 12. Thepolyolefin-based resin pre-expanded particles according to claim 3,wherein the polyolefin-based resin composition includes 0.01 parts byweight to 20 parts by weight of the sterically hindered amine etherflame retardant expressed by the general formula (1) and 0.01 parts byweight to 10 parts by weight of the phosphoric ester with respect to 100parts by weight of the polyolefin-based resin.
 13. The polyolefin-basedresin pre-expanded particles according to claim 3, wherein thepolyolefin-based resin is a polypropylene-based resin.
 14. Thepolyolefin-based resin pre-expanded particles according to claim 9,wherein the blowing agent is at least one selected from the groupconsisting of isobutane and normal butane.
 15. The polyolefin-basedresin pre-expanded particles according to claim 9, wherein the blowingagent is carbon dioxide.
 16. The polyolefin-based resin pre-expandedparticles according to claim 9, wherein the polyolefin-based resincomposition includes 0.01 parts by weight to 20 parts by weight of thesterically hindered amine ether flame retardant expressed by the generalformula (1) and 0.01 parts by weight to 10 parts by weight of thephosphoric ester with respect to 100 parts by weight of thepolyolefin-based resin.
 17. The polyolefin-based resin pre-expandedparticles according to claim 9, wherein the polyolefin-based resin is apolypropylene-based resin.